Ana and TD 3 take aim at the Lesser Antilles

Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.

Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.

Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD

Tropical Depression Three forms, could be Bill later todayQuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.

Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.

Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.

Can't believe after three years on the board (mostly lurking) I am going to ask this question. Do any of the systems show any evidence of wanting to hit Florida on the east side (central Florida). I really am reading the updates, but every time I think I get a grasp of one of the systems, one of the other ones is screaming for attention.

Quoting nash28:Once again, for the cheap seats ladies and gentlemen, the models right now past five days are crap. Crap. It is a TS. A low level flow TS. Anyone with eyes and a steering flow map can see what the steering flow will be like for the next few days. Anyone guessing after that, INCLUDING the models is just guessing. It's all about the AB high, the AB high bridging with the NE ridge and the trough.

http://icons-pe.wunderground.com/data/images/at200903_model.gifthe models are still pulling it to be a fish storm but.... like Ike... anything can happen.... I Ike was not good I was without light for a week.

After cruising through the 11pm local news, the mets here in Savannah are already going bonkers over Bill. One even went so far as to say "Bill will definitely be affecting our area weather next weekend."

Once again, for the cheap seats ladies and gentlemen, the models right now past five days are crap. Crap. It is a TS. A low level flow TS. Anyone with eyes and a steering flow map can see what the steering flow will be like for the next few days. Anyone guessing after that, INCLUDING the models is just guessing. It's all about the AB high, the AB high bridging with the NE ridge and the trough.

I think that Ana may pull an Ernesto on us. I think that it will strengthen to about 60 mph by the time it reaches Hispaniola, weaken to a depression as it passes through Hispaniola and Cuba, and restrengthen to about 65-70 mph by the time it reaches the Gulf Coast.

but the storm isnt moving like models are forecasting, they are forecasting it to be moving NW shortly and then out to sea, its moving w-wsw right now

The NHC track, following the models, shows Bill continuing to move WSW for a while yet before gradually turning to W and then WNW. Nothing is based on it suddenly changing course to 315, so nothing is disproven by it not having done so.

This track and the discussion are both half an hour old and both take the current 270 motion into account.

Quoting lopaka001:IKE is that Jimmy and Robert in your avatar?My LCD screen is huge it is so hard to tell for me with these high rez settings..

LOL got a question for everyone and no this is not a joke!I have a wedding to attend in the Caicos Island on Tuesdayand it is on the beach something tells me it is going to be interesting should I cancel my trip??Anyone care to take a stab at this hehe..

Yup...Zeppelin...

Should be okay on Tuesday. NHC shows Ana getting ripped apart over DR/Haiti Tuesday, IF it's still around til Tuesday.

Quoting nyhurricaneboy:I know this may be going out too far in the forecast period, but do you think that Bill could pose a threat to the Northeast, specifically the NYC area? The models are indicating that this may occur about a week and a half out.

I have been indicating a possibility of a Northeast landfall, it's still possible, keep monitoring this system closely.

Quoting Funkadelic:Well I guess you and I are the only ones noticing the models are wrong at this point. Right now its moving fast west at 16mph with jogs to the south. That is not going to help it recurve.

Keith's note: Sources report that the LRO team has assembled a series of polar images into a mosaic but they are refusing to release these mosaics - or the images - to interested parties - or to the public.